The fabrication of an integrated circuit, display or disc memory generally employs numerous processing steps. Each process step must be carefully monitored in order to provide an operational device. Throughout the imaging process, deposition and growth process, etching and masking process, etc., it is critical, for example, that temperature, gas flow, vacuum, pressure, chemical, gas or plasma composition and exposure distance be carefully controlled during each step. Careful attention to the various processing conditions involved in each step is a requirement of optimal semiconductor or thin film processes. Any deviation from optimal processing conditions may cause the ensuing integrated circuit or device to perform at a substandard level or, worse yet, fail completely.
Within a processing chamber, processing conditions vary. The variations in processing conditions such as temperature, gas flow rate and/or gas composition greatly affect the formation and, thus, the performance of the integrated circuit. Using a substrate to measure the processing conditions that is of the same or similar material as the integrated circuit or other device provides the most accurate measure of the conditions because the material properties of the substrate is the same as the actual circuits that will be processed. Gradients and variations exist throughout the chamber for virtually all process conditions. These gradients, therefore, also exist across the surface of a substrate, as well as below and above it. In order to precisely control processing conditions at the wafer, it is critical that measurements be taken upon the wafer and the readings be available in real time to an automated control system or operator so that the optimization of the chamber processing conditions can be readily achieved. Processing conditions include any parameter used to control semiconductor or other device fabrication or any condition a manufacturer would desire to monitor.
The PEB and PAB hotplate stations have been measured for several years with instrumented wafer apparatuses, but not with the capability to apply photoresist in any convenient or practical manner. These wafers were only required to measure temperature from the bottom of the wafer where the hotplate was, so were not designed with thinness in mind, nor were they sealed for wet environments. The standard practice is to place the instrumentation on the top surface of the wafer.
For resist dispense step, discrete probes have been used to measure the temperature of the material as it passes through the nozzle or applicator. No wafer based metrology has existed. Resist dispense stations normally rotate at up to 5000 rpm, and the resist material could damage electronics, so the apparatus needs to be mechanically balanced, sealed, and thermally balanced. This has not existed until the Integral Wafer invention.
To the best of the inventors' knowledge, there has never been an apparatus that measured the wafer temperature during exposure before. The exposure systems require strict flatness and thickness specifications, so a thin planar architecture is required.
Furthermore, post processing of the wafer may induce overlay distortion effects. To the best of the inventors' knowledge there has never been a wafer-based apparatus that can measure such effects in situ.
Some prior art methods use wafers that are not sealed and mechanically balanced for spinning. Consequently these methods are unable to make measurements at the resist application/dispense station. In addition, such methods use wafers that are not planar so exposure systems. Furthermore, previous sensor wafers are not thin enough for use at an exposure station. In addition, some prior art sensor wafers are not sealed and planar enough to enable photoresist compatibility and easy removal of the photoresist. Prior art sensor wafers typically have discrete probes and are, therefore, not sufficiently spatially resolved for many applications. In addition, such wafers do not directly measure the wafer response.
It is within this context that embodiments of the present invention arise.